This invention relates to display equipment, and more particularly to a cathode ray tube used with a display system suitable for a giant color display.
In the conventional construction of giant display systems, for example, electric light display boards used with baseball fields, apparatus for displaying advertising pictures or the like on the roof top or wall surface of buildings, etc., pictures have been formed by selectively effecting the turning-on and -off of a multitude of colored electric lamps arranged in a predetermined pattern. Such display systems have had many difficult problems to be solved. For example, when electric lamps are used, light is produced by heating their filaments to red heat and therefore the light produced assumes principally a red or a white-orange color. Accordingly, in order to pick up green or blue light from those electric lamps, glass plates colored with green or blue have been used. However it has fairly been difficult to produce a large amount of the green or blue light. Also, in display systems using the electric lamps as described above, the brightness modulation of each picture element has been required to rely on means of turning a current applied to the filament of the mating electric lamp on and off, or for making the applied current variable. Further such means has had many problems, such as that its frequency response is as low as 10 Hertz or less and, in addition, the applied current is not linear with respect to the quantity of emission of light and may change the color of light emitted by the associated electric lamp. Furthermore, intermediate color tones have been difficult to produce. Moreover, since electric lamps on the order of 10 watts or more have been generally employed, a giant display which may include several ten thousand of such electric lamps arranged in a predetermined pattern has encountered problems such as large power consumption, and the total quantity of heat generated by the electric lamps becomes great and so on.
In order to solve the problems as described above, the present inventor has devised cathode ray tubes as light sources for display systems such as described above.
For example, a display system can be formed of a multitude of triads of red, green and blue cathode ray tubes arranged in rows and columns to display thereon picture images as desired. Where that electric lamps generally have an efficiency of 10 lumens per watt for converting electrical to optical energy, cathode ray tubes have an efficiency of about 100 lumens per watt. Therefore, display systems using cathode ray tubes have a better efficiency of converting electrical to optical energy by about one order of magnitude as compared with those employing electric lamps. Also since cathode ray tubes include phosphor screens luminescing in their respective colors including red, green and blue, a light source can be not only produced so as to luminesce in any desired color but also there can readily be provided light sources having a fairly good frequency response. This results in the display of animations without any hindrance. Further such light sources are optimum for displaying intermediate color tones because electrical signals applied to the light sources can faithfully change the resulting brightnesses thereof. In addition, the use of the cathode ray tubes results in an extremely low power consumption and hence an advantageous useful lifetime as compared with the use of the electric lamps wherein filament currents are variable.
From the foregoing it will readily be understood that, the use of light sources formed of cathode ray tubes provide excellent performance, reliability, cost of maintenance, power consumption etc. particularly for giant display systems.
While the use of a cathode ray tube as the light source of display systems has various advantages as described above it is seen that those advantages can be enhanced provided that the cathode ray tube can produce an optical output at its maximum without the effective diameter thereof being increased.
It is required that the cathode ray tube used with display systems of the type referred to have a satisfactory contrast even when irradiated with sun in the daytime because of the purpose and place of installation thereof.
Accordingly it is an object of the present invention to provide a new and improved cathode ray tube used with a display system to produce an optical output at its maximum and having a high contrast.